One of the products that can be generated during lubricant production via solvent processing is a high aromatic content extract product. The aromatic extraction process that generates the high aromatic content extract product is typically performed prior to hydrotreating of the lubricant feed. As a result, the high aromatic content extract product can also have elevated levels of sulfur, nitrogen, and/or metals. In some potential applications where a high aromatic content feed would be useful, the elevated levels of sulfur, nitrogen, and/or metals can pose difficulties for use of an aromatic extract product.
U.S. Pat. No. 3,790,470 describes a process for production of lubricating oils. The process includes hydrocracking of a suitable lubricant boiling range feedstock. The yield of hydrocracked oil (in the lubricant boiling range) is reported as being about 70% in an example. A solvent extraction is then performed on the hydrocracked effluent to produce a raffinate with reduced aromatic content and an extract with increased aromatic content. The extract is then exposed to catalytic hydrogenation conditions. The hydrogenated extract is then combined with the raffinate to improve the overall yield of lubricant base oil from the process. Although the viscosity index of the hydrogenated extract is relatively low, the viscosity index of the final lubricant base oil product is only modestly lower than the viscosity index of the raffinate.